In the art of photolithography which has been useful for many years in the construction of semiconductor integrated circuits and devices, ultraviolet radiation has been useful as a means for exposing and developing a variety of known and commercially available photoresist materials. However, as a result of the diffracton limitations of standard photolithographic mask making processes which use ultraviolet radiation, the minimum resolution obtainable using this prior art process is about 1 micrometer.
To improve upon this resolution limitation of prior art photolithographic processes using ultraviolet radiation, two technologies have evolved. One of these technologies is known as "X-ray lithography" and is disclosed, for example, in an article by Henry I. Smith entitled "Fabrication Techniques for Surface Acoustic Wave and Thin Film Optical Devices" Proceeding of the IEEE, Vol. 62 No. 10, October, 1974, pages 1361-1387. A second technology which also involves an alternative approach to ultraviolet (UV) photolithography for mask fabrication is known as "electron projection lithography", and one process of the latter type is disclosed, for example, in U.S. Pat. No. 3,672,987 issued to T. W. O'Keeffe et al.
The above two technologies have demonstrated certain advantages over ultraviolet photolithography as a method of mask fabrication, and may in some instances overcome the diffraction limitations and achievable resolutions characteristic of UV processes. However, both the X-ray and electron projection processes are time consuming and do not readily lend themselves to large scale batch fabrication processing. For example, the time required for X-rays to expose patterns in a positive resist layer is prohibitively long and may require several hours to complete. Additionally, adverse proximity effects occur when exposing resist layers with closely spaced electron beams. Both of these latter disadvantages have been eliminated by the present invention.